The present invention is generally directed to toner processes, and more specifically to aggregation and coalescence processes for the preparation of toner compositions ! n embodiments, the present invention is directed to the preparation of toners without the utilization of the known pulverization and/or classification methods, rendering the present process economical and wherein toner compositions with a volume average diameter of from about 1 to about 25, and preferably from 5 to about 15 microns in volume average diameter and narrow GSD of, for example, from about 1.18 to about 1.26 as measured on the Coulter Counter, can be obtained. The resulting toners can be selected for known electrophotographic imaging and printing processes, including color processes, and lithography. In embodiments, the present invention is directed to a process comprised of dispersing a pigment and optionally a charge control additive and other known toner additives in an aqueous mixture containing an ionic surfactant in amount of from about 0.5 percent (weight percent throughout unless otherwise indicated) to about 10 percent and shearing this mixture with a latex mixture comprised of suspended resin particles of from, for example, about 0.01 micron to about 2 microns in volume average diameter in an aqueous solution containing a counterionic surfactant in amounts of from about 1 percent to about 10 percent with opposite charge to the ionic surfactant of the pigment dispersion, and nonionic surfactant in amount of from 1 percent to about 5 percent, thereby causing a flocculation of resin particles, pigment particles and optional charge control particles, followed by heating in a sensitive critical region of the resin Tg, where the temperature is in the range of from about 0.degree. C. to about 10.degree. C., and preferably about 5 to about 8.degree. C. above the resin Tg while stirring of the flocculent mixture, which is believed to form statically bound aggregates of from about 4 microns to about 15 microns in average volume diameter comprised of resin, pigment and optionally charge control particles, and thereafter coalescing the aggregated particles. The size of the aforementioned statistically bonded aggregated particles increases as the temperature in this heating stage is increased in the range of 0.degree. C. to about 10.degree. C. of the resin Tg. The aggregating of submicron latex and pigment particles is believed to be a kinetically controlled process. Since the aggregation is performed at temperatures about equal or above the resin Tg, the aggregation process is hence rendered very sensitive and careful temperature control is essential. The higher the temperature of the stirring to form the aggregates the bigger the particle size, for example at 50.degree. C. a particle size of about 6 microns is obtained, while at temperatures of 62.degree. C. a particle size of about 10 microns is obtained with narrow particle size distribution in a very short time, for example from 1 to 3 hours when the aggregation is performed at a temperatures of minus 5.degree. C. of the resin Tg, while at aggregation temperature in the range of about 8.degree. C. the time is from 1 to about 1.5 hours. Subsequently, the mixture is heated to generate toner particles with an average particle volume diameter of from about 1 to about 10 microns. It is believed that during the heating stage, tire components of aggregated particles fuse together to form composite toner particles. In another embodiment thereof, the present invention is directed to an in situ process comprised of first dispersing a pigment, such as HELIOGEN BLUE.TM. or HOSTAPERM PINK.TM., in an aqueous mixture containing a cationic surfactant, such as benzalkonium chloride (SANIZOL B-50.TM.), utilizing a high shearing device, such as a Brinkman Polytron or microfiuidizer or sonicator, thereafter shearing this mixture with a latex of suspended resin particles, such as poly(styrene butadiene acrylic acid), poly(styrene butyl acrytate acrylic acid) or PLIOTONE.TM., a poly(styrene butadiene), and which particles are, for example, of a size ranging from about 0.01 to about 0.5 micron in average volume diameter as measured by the Brookhaven nanosizer in an aqueous surfactant mixture containing an arionic surfactant such as sodium dodecylbenzene sulfonate, for example NEOGEN R.TM. or NEOGEN SC.TM., and nonionic surfactant such as alkyl phenoxy poly(ethylenoxy)ethanol, for example IGEPAL 897.TM. or ANTAROX 897.TM., thereby resulting in a flocculation, or heterocoagulation of the resin particles with the pigment particles; arid which on further stirring while heating results in the formation of statically bound aggregates ranging in size of from about 5 microns to about 15 microns in average diameter size as measured by the Coulter Counter (Microsizer II) where the size of aggregated particles is controlled by heating in the very sensitive regions to the resin Tg, for example in the range of 54.degree. C. to 64.degree. C. The process of heating in the range of 0.degree. C. to 10.degree. C. above the resin Tg to form statically bound aggregates is accomplished for an effective time of, for example, preferably about 1 to 1.5 hours. The aforementioned toners are especially useful for the development of colored images with excellent line and solid resolution, and wherein substantially no background deposits are present. While not being desired to be limited by theory, it is believed that the flocculation or heterocoagulation is caused by the neutralization of the pigment mixture containing the pigment and cationic surfactant absorbed on the pigment surface with the resin mixture containing the resin particles and anionic surfactant absorbed on the resin particle. This process is kinetically controlled and an increase, for example, from about 54.degree. C. to 64.degree. C. in temperature increases the flocculation, and hence aggregated particle size from about 5 to 10 microns while achieving a narrow particle size distribution providing, for example, a GSD of about 1.20. Thereafter, heating the aggregates, for example 11 to 50.degree. C. above the resin Tg, fuses the aggregated particles or coalesces the particles to enable the formation of toner composites of polymer and pigments, and optionally charge control agents. Furthermore, in other embodiments the ionic surfactants can be exchanged, such that the pigment mixture contains the pigment particle and anionic surfactant, and the suspended resin particle mixture contains the resin particles and cationic surfactant; followed by the ensuing steps as illustrated herein to enable flocculation by charge neutralization while shearing; and thereby forming statically bounded aggregate particles by stirring and heating in the critical sensitive regions of the resin Tg, for example in the range of 50.degree. C. to 65.degree. C. and specifically in the range of 54.degree. C. to 64.degree. C., and thereafter, that is when the aggregates are formed, heating in the range of 11.degree. C. to 50.degree. C. above the resin Tg to form stable toner composite particles. Of importance with respect to the processes of the present invention in embodiments is computer controlling the temperature of the heating to form the aggregates, since the temperature affects the rate of aggregation, the size of the aggregates and the particle size distribution of aggregates.
In reprographic technologies, such as xerographic and ionographic devices, toners with volume average diameter particle sizes of from about 9 microns to about 20 microns are effectively utilized. Moreover, in some xerographic technologies, such as the high volume Xerox Corporation 5090 copier duplicator, high resolution characteristics and low image noise are highly desired, and can be attained utilizing the small sized toners of the present invention with, for example, a volume average particle of 5 to 15 microns and preferably less 5 to 9 microns and with narrow geometric size distribution (GSD) of from about 1.16 to about 1.3. Additionally, in some xerographic systems wherein process color is utilized such as pictorial color applications, small particle size colored toilers of from about 3 to about 9 microns are highly desired to avoid paper curling. Paper curling is especially observed in pictorial or process color applications wherein three to four layers of toners are transferred and fused onto paper. During the fusing step, moisture is driven off from the paper due to the high fusing temperatures of from about 130.degree. C. to about 160.degree. C. applied to the paper from the fuser. Where only one layer of toner is present, such as in black or in highlight xerographic applications, the amount of moisture driven off during fusing is reabsorbed proportionally by paper and the resulting print remains relatively flat with minimal curl. In pictorial color process applications wherein three to four colored toner layers are present, a thicker toner plastic level present after the fusing step inhibits the paper from sufficiently absorbing the moisture lost during the fusing step, and image paper curling results. These and other disadvantages and problems are avoided or minimized with the toners and processes of the present invention. It is preferable to use small toner particle sizes, such as from about 4 to about 7 microns, and with higher pigment loading such as from about 5 to about 12 percent t3y weight of toner, such that the mass of toner layers deposited onto paper is reduced to obtain the same quality of image and resulting in a thinner plastic toner layer onto paper after fusing, thereby minimizing or avoiding paper curling. Toners prepared in accordance with the present invention enable the use of lower fusing temperatures, such as from about 120 to about 150.degree. C., thereby avoiding or minimizing paper curl. Lower fusing temperatures minimize the loss of moisture from paper, thereby reducing or eliminating paper curl. Furthermore, in process color applications and especially in pictorial color applications, toner to paper gloss matching is highly desirable. Gloss matching is referred to as matching the gloss of the toner image to the gloss of the paper. For example, when a low gloss image of preferably from about 1 to about 30 gloss is desired, low gloss paper is utilized, such as from about 1 to about 30 gloss units as measured by the Gardner Gloss metering unit, and which after image formation with small particle size toners of from about 3 to about 5 microns and fixing thereafter results in a low gloss toner image of from about 1 to about 30 gloss units as measured by the Gardner Gloss metering unit. Alternatively, if higher image gloss is desired, such as from greater than about 30 to about 60 gloss units as measured by the Gardner Gloss metering unit, higher gloss paper is utilized such as from greater than about 30 to about 60 gloss units.
Numerous processes are known for the preparation of toners, such as, for example, conventional processes wherein a resin is melt kneaded or extruded with a pigment, micronized and pulverized to provide toner particles with an volume average particle diameter of from about 9 microns to about 20 microns and with broad geometric size distribution of from about 1.4 to about 1.7. In such processes, it is usually necessary to subject the aforementioned toners to a classification procedure such that the geometric size distribution of from about 1.2 to about 1.4 is attained. Also, in the aforementioned conventional process, low toner yields after classifications may be obtained. Generally, during the preparation of toners with average particle size diameters of from about 11 microns to about 15 microns, toner yields range from about 70 percent to about 85 percent after classification. Additionally, during the preparation of smaller sized toners with particle sizes of from about 5 microns to about 10 microns, lower toner yields are obtained after classification, such as from about 50 percent to about 70 percent. With the processes of the present invention, in embodiments small average particle sizes of, for example, from about 5 microns to about 12 microns, are attained without resorting to classification processes, and narrow geometric size distributions are attained, such as from about 1.16 to about 1.26. High toner yields are also attained such as from about 90 percent to about 98 percent in embodiments. In addition, by the toner particle preparation process of the present invention in embodiments, small particle size toners of from about 5 microns to about 10 microns can be economically prepared in high yields such as from about 90 percent to about 98 percent by weight based on the weight of all the toner material ingredients, such as toner resin and pigment.
There is illustrated in U.S. Pat. No. 4,996,127 a toner of associated particles of secondary particles comprising primary particles of a polymer having acidic or basic polar groups and a coloring agent. The polymers selected for the toners of the '127 patent can be prepared by an emulsion polymerization method, see for example columns 4 and 5 of this patent. In column 7 of this '127 patent, it is indicated that the toner can be prepared by mixing the required amount of coloring agent and optional charge additive with an emulsion of the polymer having an acidic or basic polar group obtained by emulsion polymerization. Also, note column 9, lines 50 to 55, wherein a polar monomer such as acrylic acid in the emulsion resin is necessary, and toner preparation is not obtained without the use, for example, of acrylic acid polar group, see Comparative Example I. The process of the present invention does not need to utilize polymer polar acid groups, and toners can be prepared with resins such as poly(styrenebutadiene) or PLIOTONE.TM. without containing polar acid groups. Additionally, the process of the '127 patent does not utilize counterionic surfactant and flocculation process as does the present invention, and does not use a counterionic surfactant for dispersing the pigment. In U.S. Pat. No. 4,983,488, a process for the preparation of toners by the polymerization of a polymerizable monomer dispersed by emulsification in the presence of a colorant and/or a magnetic powder to prepare a principal resin component and then effecting coagulation of the resulting polymerization liquid in such a manner that the particles in the liquid after coagulation have diameters suitable for a toner. It is indicated in column 9 of this patent that coagulated particles of 1 to 100, and particularly 3 to 70, are obtained. This process is thus directed to the use of coagulants, such as inorganic magnesium sulfate which results in the formation of particles with wide GSD. Furthermore, the '488 patent does not disclose the process of counterionic, for example controlled aggregation is obtained by changing the counterionic strength, flocculation of the present invention. Similarly, the aforementioned disadvantages, for example poor GSD are obtained, hence classification is required resulting in low yields, are illustrated in other prior art, such as U.S. Pat. No. 4,797,339, wherein there is disclosed a process for the preparation of toners by resin emulsion polymerization, wherein similar to the '127 patent polar resins of opposite charges are selected, and wherein flocculation as in the present invention is not disclosed; and U.S. Pat. No. 4,558,108, wherein there is disclosed a process for the preparation of a copolymer of styrene and butadiene by specific suspension polymerization. Other prior art that may be of interest includes U.S. Pat. Nos. 3,674,736; 4,137,188 and 5,066,560.
The process described in the present application has several advantages as indicated herein including the effective preparation of small toner particles with narrow particle size distribution as a result of no classification; yields of toner are high; large amounts of power consumption are avoided; the process can be completed in rapid times therefore rendering it attractive and economical; and it is a controllable process since the particle size of the toner can be tightly controlled by controlling the temperature of the aggregation.
In now U.S. Pat No. 5,290,654, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toners comprised of dispersing a polymer solution comprised of an organic solvent and a polyester, and homogenizing and heating the mixture to remove the solvent and thereby form toner composites. Additionally, there is disclosed in copending application U.S. Ser. No. 936,471, now U.S. Pat. No. 5,278,028, the disclosure of which is totally incorporated herein by reference, a process for the preparation of in situ toners comprising a halogenization procedure which chlorinates the outer surface of the toner and results in enhanced blocking properties. More specifically, this patent application discloses an aggregation process wherein a pigment mixture containing an ionic surfactant is added to a resin mixture containing polymer resin particles of less than 1 micron nonionic and counterionic surfactant, and thereby causing a flocculation which is dispersed to statically bound aggregates of about 0.5 to about 5 microns in volume diameter as measured by the Coulter Counter, and thereafter heating to form toner composites or toner compositions of from about 3 to about 7 microns in volume diameter and narrow geometric size distribution of from about 1.2 to about 1.4, as measured by the Coulter Counter, and which exhibit, for example, low fixing temperature of from about 125.degree. C. to about 150.degree. C., low paper curling, and image to paper gloss matching.
In U.S. Pat. No. 5,308,734 (D/92576), the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions which comprises generating an aqueous dispersion of toner fines, ionic surfactant and nonionic surfactant, adding thereto a counterionic surfactant with a polarity opposite to that of the ionic surfactant, homogenizing and stirring the mixture, and heating to provide for coalescence of the toner fine particles.
In copending patent application U.S. Ser. No. 082,651, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions with controlled particle size comprising:
(i) preparing a pigment dispersion in water, which dispersion is comprised of pigment, an ionic surfactant and an optional charge control agent;
(ii) shearing at high speeds the pigment dispersion with a polymeric latex comprised of resin, a counterionic surfactant with a charge polarity of opposite sign to that of the ionic surfactant, and a nonionic surfactant thereby forming a uniform homogeneous blend dispersion comprised of resin, pigment, and optional charge agent;
(iii) heating the above sheared homogeneous blend below about the glass transition temperature (Tg) of the resin while continuously stirring to form electrostatically bound toner size aggregates with a narrow particle size distribution;
(iv) heating the statically bound aggregated particles above about the Tg of the resin particles to provide coalesced toner comprised of resin, pigment and optional charge control agent, and subsequently optionally accomplishing (v) and (vi);
(v) separating the toner; and
(vi) drying the toner.
In copending patent application U.S. Ser. No. 083,146, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions with a volume median particle size of from about 1 to about 25 microns, which process comprises:
(i) preparing by emulsion polymerization an anionic charged polymeric latex of submicron particle size, and comprised of resin particles and anionic surfactant;
(ii) preparing a dispersion in water, which dispersion is comprised of optional pigment, an effective amount of cationic flocculant surfactant, and optionally a charge control agent;
(iii) shearing the dispersion (ii) with the polymeric latex thereby causing a flocculation or heterocoagulation of the formed particles of optional pigment, resin and charge control agent to form a high viscosity gel in which solid particles are uniformly dispersed;
(iv) stirring the above gel comprised of latex particles, and oppositely charged dispersion particles for an effective period of time to form electrostatically bound relatively stable toner size aggregates with narrow particle size distribution; and
(v) heating the electrostatically bound aggregated particles at a temperature above the resin glass transition temperature (Tg) thereby providing a toner composition comprised of resin, optional pigment and optional charge control agent.
In copending patent application U.S. Ser. No. 083,157, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions with controlled particle size comprising:
(i) preparing a pigment dispersion in water, which dispersion is comprised of a pigment, an ionic surfactant in amounts of from about 0.5 to about 10 percent by weight of water, and an optional charge control agent;
(ii) shearing the pigment dispersion with a latex mixture comprised of a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant, a nonionic surfactant and resin particles, thereby causing a flocculation or heterocoagulation of the formed particles of pigment, resin and charge control agent;
(iii) stirring the resulting sheared viscous mixture of (ii) at from about 300 to about 1,000 revolutions per minute to form electrostatically bound substantially stable toner size aggregates with a narrow particle size distribution;
(iv) reducing the stirring speed in (iii) to from about 100 to about 600 revolutions per minute and subsequently adding further anionic or nonionic surfactant in the range of from about 0.1 to about 10 percent by weight of water to control, prevent, or minimize further growth or enlargement of the particles in the coalescence step (iii); and
(v) heating and coalescing from about 5 to about 50.degree. C. above about the resin glass transition temperature, Tg, which resin Tg is from between about 45 to about 90.degree. C. and preferably from between about 50 and about 80.degree. C., the statically bound aggregated particles to form said toner composition comprised of resin, pigment and optional charge control agent.
In copending patent application U.S. Serial No. 082,741, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions with controlled particle size and selected morphology comprising
(i) preparing a pigment dispersion in water, which dispersion is comprised of pigment, ionic surfactant, and optionally a charge control agent;
(ii) shearing the pigment dispersion with a polymeric latex comprised of resin of submicron size, a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant and a nonionic surfactant thereby causing a flocculation or heterocoagulation of the formed particles of pigment, resin and charge control agent, and generating a uniform blend dispersion of solids of resin, pigment, and optional charge control agent in the water and surfactants;
(iii) (a) continuously stirring and heating the above sheared blend to form electrostatically bound toner size aggregates; or
(iii) (b) further shearing the above blend to form electrostatically bound well packed aggregates; or
(iii) (c) continuously shearing the above blend, while heating to form aggregated flake-like particles;
(iv) heating the above formed aggregated particles about above the Tg of the resin to provide coalesced particles of toner; and optionally
(v) separating the toner particles from water and surfactants; and
(vi) drying the toner particles.
In copending patent application U.S. Ser. No. 082,660, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions comprising:
(i) preparing a pigment dispersion, which dispersion is comprised of a pigment, an ionic surfactant, and optionally a charge control agent;
(ii) shearing said pigment dispersion with a latex or emulsion blend comprised of resin, a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant and a nonionic surfactant;
(iii) heating the above sheared blend below about the glass transition temperature (Tg) of the resin to form electrostatically bound toner size aggregates with a narrow particle size distribution; and
(iv) heating said bound aggregates above about the Tg of the resin.
In copending patent application U.S. Serial No. 083,116, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions comprising
(i) preparing a pigment dispersion in water, which dispersion is comprised of pigment, a counterionic surfactant with a charge polarity of opposite sign to the anionic surfactant of (ii) and optionally a charge control agent;
(ii) shearing the pigment dispersion with a latex comprised of resin, anionic surfactant, nonionic surfactant, and water; and wherein the latex solids content, which solids are comprised of resin, is from about 50 weight percent to about 20 weight percent thereby causing a flocculation or heterocoagulation of the formed particles of pigment, resin and optional charge control agent; diluting with water to form a dispersion of total solids of from about 30 weight percent to 1 weight percent, which total solids are comprised of resin, pigment and optional charge control agent contained in a mixture of said nonionic, anionic and cationic surfactants;
(iii) heating the above sheared blend at a temperature of from about 5 to about 25.degree. C. below about the glass transition temperature (Tg) of the resin while continuously stirring to form toner sized aggregates with a narrow size dispersity; and
(iv) heating the electrostatically bound aggregated particles at a temperature of from about 5 to about 50.degree. C. above about the Tg of the resin to provide a toner composition comprised of resin, pigment and optionally a charge control agent.
There are a number of differences of the processes of the present invention compared to those illustrated in the aforementioned copending patent applications including, for example, the following. Different particle sizes especially 5 microns and up, for example in the range of 5 to 15 microns, can be prepared by altering the aggregation temperature (step iii) where the temperature is in the sensitive critical region of the resin Tg, which is, for example, between 54 and 64.degree. C. Another advantage of the present invention is that the latex solids comprised of resin and pigment particles concentration does not need to be reduced in embodiments, for example from 12 percent down to 6 percent. In the present invention, the latex concentration can be retained in embodiments at about 12 percent.